text:
Is flying during the day safer than flying at night?
Is there any correlation between night or day flight time and rate of accidents?
To me it seems that there should not be a difference. If an airplane needs to execute an emergency landing, it has to do it at an airport which is illuminated at night.
However, what if the pilot needs some ground visuals to navigate, for example, because the instrument are not working similar to the Air France Flight 447.
Edit
I only mean commercial airline flights done by planes such as airbus a320/321/330 or Boeing 737-800.

AF447 occurred in IMC. Probably would have happened in the daytime too

Been doing a layman's research on air India flight 855 that crashed near Bombay (Mumbai now) in new year 1978. It went down into the Arabian sea just 3 Km away after take off. The night factor (about 8.45 pm) may have contributed to the cause inconclusively pointed at pilot disorientation /instrument failure. They didn't know they were banking more and more to the left, the report says. (not the exact words). It was a Boeing 747 (not sure) bom - dubai.

FWIW, it is possible to land at an unlighted airport.  Not that I'd recommend it, you understand, but it's way preferrable to crashing in a randomly-selected bit of terrain.

There is not enough illumination . I think there was a crashe where pilot landed on wrong road and on that road there was another plane . If there was daytime, good visibility, he would have seen another plane from the bigger distance I think.

First, I should reiterate that commercial flights at any time of day are extremely safe.  Saying flights at night are more dangerous is like saying going to buy groceries at night is more dangerous.  It may be true, but it shouldn't be something a traveler worries about.
It seems from the available data that accidents are at least more dangerous at night, even though I can't tell if accidents are more likely. Certain kinds of accidents, like weather-related accidents or disorientation, are also more common at night than during the day.
A great source for this is an incident database that you can download from the NTSB database of aviation incidents (there's a link on the page for downloadable datasets).   Opening the downloadable dataset in Access lets you find statistics for whatever criteria you want. I filtered for records with aircraft operating commercially (not general aviation or commuter) with light conditions (like day vs. night) available.
In this dataset, 1562 incidents occurred during daylight, dawn, or dusk, and 635 occurred at night, or about 29% of all incidents (Incidents include procedural violations and near-misses as well as accidents that cause damage or injury).  To figure out how likely an accident is at night versus the day, we would need to get data on traffic volume that matches the dataset I'm using.  Unfortunately, I don't have that information, but we can look at other statistics to see whether these night incidents are more serious.
Of those incidents, 5.6% of incidents during the day had at least 1 fatality and 8.9% of night incidents had at least 1 fatality.  Also, only 1.6% of incidents during the day had at least ten fatalities compared to 2.5% at night. This confirms that night incidents are slightly more likely to be fatal.  It's also worth noting that among accidents reported as "dark night," 9.7% were fatal, showing only a slight increase from other night conditions.  The percentage of total fatalities that happened at night is a bad statistic because a large amount of those fatalities come from a few large crashes.

In a closely related statistic, 49% of the incidents during the day were not classified as "accidents," compared to 41% at night.  This means the margin between an incident and a full-scale accident is narrower at night.
Some kinds of incidents are also far more common at night than during the day. 27.4% of incidents were marked as involving a weather condition at day versus 38.7% at night (which is surprising considering that thunderstorms and turbulence are less common at night).  Other incident codes that represent a larger share of the incidents at night include "became lost or disoriented," "minimum descent altitude," "crew/group coordination," "airport facilities," "object," and, unsurprisingly, "light condition."  Surprisingly, the following were not unusually common codes for night incidents: "terrain," "anti-ice," and "taxiway lighting" (wait what?).  Some of these codes (like for taxiway lighting related incidents) are so rare that the statistics for them are unreliable.
I looked at the set of flights recorded by the NTSB since 1982 with light condition recorded and FAR part listed as 121, 125, 129, or "NUSC" (I make no guarantees that this dataset is an unbiased representation of all incidents since many crashes are excluded from these criteria).  Dawn and dusk were considered during the day when counting.  I'm counting by plane technically, not by incident.

Great research! May be worth noting, that the increase in night fatalities be simply because an injured person is harder to find in the dark. For example, someone exits the plane in shock, and wonders off away from responders instead of toward them, responders don't see the person because it's dark and they're focused on those they can see (until the passenger list is counted and they realize someone is missing).

For that matter, going to get groceries is probably more dangerous than flying no matter what time of day it is, assuming that you drive to and from the grocery store.

There's not much statistical evidence to say conclusively. However, the FAA say that in general aviation 69% of crashes at night cause pilot fatality compared to 59% during day. Various FAA/NTSB reports state (f.ex: This) that there's more crashes during day than night but that's hard to interpret: There's a lot more planes in the air during the day.
For commercial aviation it's even harder to conclude anything. But this says that commercial aircraft fly around 1km closer to bad weather at night compared to during the day, which gives a rough indication that weather-related incidents may be more common at night.

Answering your second paragraph, there may be more weather-related incidents at night, but it may just mean that pilots are over-cautious when they can see the weather coming.

Or it may mean that they're not cautious enough at night ;) Like I said, there's very little data one way or the other.

@sp1 I can't see 'not cautious enough.' Why would they be less cautious? More likely reliance on weather radar which can be tricky to use and can mislead pilots.

@TomMcW Human factors: If pilots see a storm out their window that looks scary then they'll often deviate by a larger margin than if they can only see it as a red blob on the radar.

more flight at daytime . So take count of crashes and divid by number of flights,. Take number of crashes at day and divide by number of flihgts per day. And lets see what happens

I don't know about statistics. Airliner crash stats are fraught with problems. The extreme rarity of the events means that any numbers suffer from small sample size.
Flying at night offers a lot of extra challenges compared to daytime.
Controlled flight into terrain (CFIT)
This is the accident category that is the biggest contributor to nighttime accidents. Many CFIT accidents occur in poor weather conditions (IMC) day and night, but there have been numerous incidents of CFIT in clear weather at night. The simple truth is, if they can see something they are far less likely to fly into it.
Weather
At night pilots have to rely on radar to avoid dangerous weather. Weather radar is not a simple thing to use. Pilots have to be trained how to use it effectively. But even in the best hands weather radar can still hide problems and be misleading. This is true during the day also, but the added ability to look out the window and see conditions can help pilots fly around storm systems.
I'm sure in some situations it would also be easier to see airframe icing during the day.
Spatial disorientation
This phenomena can be a real killer and even experienced pilots can succumb to it. It can occur during the day in IMC, but often at night, especially over open water, clear skies can be no help.
Optical illusions
There are some types of optical illusion that only occur at night. One example is the black hole effect
Pilot fatigue
Lack of sunlight is known to contribute to sleepiness.
Example accidents
Here is a short list of accidents that almost certainly wouldn't have happened during the daytime. These are just the ones I can think of off the top of my head, mostly ones I've seen on Mayday/Air Emergency/Air Disasters/Air Crash Investigation (I have no idea why that show has four different titles).

Korean Airlines 801
Aeroperu 603
Flash Airlines 604
Air Inter 148
Fedex 1478
Cross Air 3597
American Airlines 965
Eastern Airlines 401
Avianca 11
VASP 168

I can't really even think of a daytime crash that wouldn't have happened in the same conditions at night. Maybe Air New Zealand 901 that crashed into Mt. Erebus in Antarctica due to a daytime optical illusion.

In case of CFIT, how could it be possible that a pilot crash a plane flying at 10Km above the earth to the ground by mistake? Doesn't he have the instrument to tell him the altitude?

In the AeroPeru accident they didn't have functioning instruments so they didn't know they were descending. The rest of the CFIT accidents happened on approach or just after takeoff. They either descended too low or got off course

This is a great list of accidents (especially the Mt. Erebus crash reference), but I'm not sure that all of these "certainly" would not have occurred during the day. Aeroperu 603, after all, wasn't the only crash due to altitude/airspeed confusion due to a blocked pitot tube. Perhaps saying it was a major contributing factor would be more accurate. That being said, aircraft can fly in zero visibility, but when the navigational aids they rely on fail, the blame isn't with the time of day- it's the problems with the navigational aids and the crew.

@CodyP I agree that no one can be 100% positive a crash wouldn't have happened during the day. and they all had other factors (rarely does a plane crash for only one reason). But in all of these simply seeing the terrain or ocean would have prevented it. They all happened in good weather.

@CodyP pitot failure crashes have all been either night or in imc

@CodyP Keep in mind, I'm not saying that night flying is unsafe. All IFR flights must be capable of flying in zero visibility down to their landing limits. I'm just saying that there are more challenges at night than during the day.

@TomMcW True.  It's safe to say that VASP 168, for example,  probably wouldn't have happened if the pilot could see the mountain in front of him that he didn't believe was there.

Not sure the Flash604 incident would have been prevented by being in daylight. The ASN report indicates that the investigation was inconclusive and no real reason was found. I suppose that disorientation due to being in the dark may have allowed the plane to reach its inverted, nose-down position in the first place, but the crew seems to have recognized there was a situation and started to react appropriately nearly immediately.

@FreeMan I hadn't read the ASN report. The cause was disputed between the Egyptian authorities, who concluded it was an undetermined aircraft malfunction and the NTSB and BEA that concluded it was spatial disorientation

@TomMcW: Which just goes to show that descending below glideslope or going off course is more dangerous if you can't see that the ground\sea is closer than it should be.

From a pilot's point of view, yes.
I spent 25 years as a commercial pilot, and night flights always had the worst fatalities. I know of several instances where flights were cancelled due to the pilot(s) not turning up due to this fear.
During the night, it is harder to make out things like hills, mountains, power stations etc. Basically, the pilot can't see the things he wants to avoid!
I always prefer fly day vs night simply due to everything being so much clearer.

I always prefer driving at day, than at night , so probably same with flying.


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Are there any new orders for the B747 passenger version?
I was reading an article about the shortcoming and decline in the use of the A380, based on the modification of the model to move people, and there is a comment saying that both the 380 and 747 are already halting production, and the only one surviving is the 747-8 in freighter mode.
Also I didn't performed an extensive search, but I can't find orders later than 2018.
Does this mean no one is operating the 747-8 in passenger flights anymore?

I'm not sure if you're asking a) if there are open orders for the 747-8 passenger variation, or b) is anyone still operating the 747-8 for passengers. Can you make that a little clearer in your question?

to add to @Pondlife comment, you may also be asking if there is no more possibility to buy a 747-8I, taking into account the second-hand market (which may receive not-so-old passenger quad-jet due to premature renew of airlines fleet while resuming operation after the covid19 crisis)

I think this answer answers your question (not sure, you question is not clear enough right now).

Are you asking about operating already built 747-8s in passenger service or are you asking about purchasing new 747-8s for passenger service? KAL's HL7644 seems to be configured for passenger service as of April 2019. It could have been converted to cargo only in the past year, though. There are newer pics (Jan 2020) of the right side of the plane showing passenger only doors. I would think the cargo doors would be installed on the left, but I'm not certain. [Con't]

...Therefore, there appears to be at least one 747-8 still in passenger service. This answers the question in your question, but that's a different question than in your title. Would you please clarify.

this question will always be out of date as orders can change through time

I will assume that you have conflated "orders for 747s" with "airlines operating 747s", and you are actually asking if any airline has a passenger 747 on order with Boeing.
Per Boeing's Order & Deliveries page, there are no unfulfilled 747-8 (the passenger variant) orders.

You can generate the report by going to http://www.boeing.com/commercial/#/orders-deliveries, selecting "Report by Model", and then selecting "747-8" for "Current Model Series".

Pure commentary: Only 47 of the latest model produced. That's so sad for an aircraft series with such a great history.

It really is, I can only hope that the few carriers that have them will keep them in passenger operations for their natural life. But the economic reality may make that impossible.

No, it seems the twin engine long range jets are filling that role sufficiently.

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What is the best way to keep logbook entries backed up?
What is the best way to keep logbook entries backed up?
Should a photocopied or scanned image on a computer suffice? Can an Excel spreadsheet or other software/apps be used? In case a logbook is lost or (unfortunately) destroyed, should all entries from the backup be rewritten in a new logbook?
Also, when one has 100s or 1000s of hours, spreading over several logbooks, how much importance the older logbooks will have? Would someone go over every page to make sure that this individual actually have 1375.2 hours (as an example)?

This article talks about some options for electronic record keeping.

The FAA requirements are for the information to be logged, without specifying the details of how it is logged.
It's OK to use electronic log books, and multiple log books. Scanned images are as good as photocopies. Just print them if you ever need them on paper. Some items are required to be signed, so scanned signatures and endorsements may be necessary in an electronic logbook.
The older the information, the less its importance. Log books are normally examined to see if what you're doing is legal, checking ratings, currency, training and reviews, etc. If you are flying without required night or IFR currency, for example, it is conceivable that they'd want to check previous flights to see how often that has happened in the past.
An insurance company might want to make sure you've got the hours you claim, but the FAA's interest is to see if you are legal.

If you're comfortable with using a tablet device as a logbook to enter everything electronically without using paper (unless a printed copy is needed) there are professional logbook apps available such as Logbook Pro Mobile.

Every few years, I put a digital camera on a tripod and photograph all the logbook pages since my last "backup". I still keep my official logbook with pen and paper. I'm old-school that way. Technology changes. Formats change. But a paper-and-pen logbook will be readable forever.

Note also: every time you get a flight physical or apply for a new license or rating, the FAA asks for your current logbook values. This gets recorded and becomes official, so if you lose your logbook, you can write to them and ask for the last numbers they had recorded. You can use this as the "start" point for your new logbooks if nothing else is available.

And finally: you have to keep a logbook, but you don't have to carry it. Mine never leaves my office at home unless I need to bring it with me for an instructor or examiner to write in.

@xpda OK for the FAA, but do you have information for non-US regulation?

I don't know of any international regulations for logbooks. I think they are country specific. JAA and EASA regulations allow electronic logbooks:  http://www.easa-logbook.eu/features.html

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text:
How are light weight fillers made for fixing dents on airplane wings?
Say an airplane wing was damaged by hail, it's really costly to replace the panel due to inaccessible rivets and what not, and the back of the panel is inaccessible to mechanically remove the dent.  How are light weight fillers made to fill the gap? Not like the heavy stuff like Bondo that is (was?) used to fill dents on cars, piled on and then sanded smooth.  Airplanes need something light weight.

I don't know of any fillers used on aircraft skins. The problem is that the skin isn't rigid enough to hold a filler like bondo is for cars. When aircraft are hail-damaged they either fly with "speed dimples", or they are reskinned.

If you want a long read on FAA authorized repair procedures give that a go.

I’m not an A&P but I’ve worked a lot on small airplanes and I would be shocked if any filler was approved for wing repair. It would be appropriate for non-structural repairs like on fiberglass fairings and wing tips but not on the wings, tail, or fuselage.

Poly-Fiber's SuperFil has long been used on aircraft. It adheres very well to aluminum, wood, and composites. Many people specifically use it to fill seams and low points specifically because it adheres well, is easily applied, has a 60 minute pot life and cures to sandable condition in 12 hours.

Lightweight body fillers such as Poly-Fiber's SuperFil are two-part epoxy fillers. The reason they are lightweight is that a significant portion of the filler in the epoxy is composed of microballoons, also known as glass microspheres.

This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post. - From Review

@Sean The core of the question is "How are light weight fillers made to fill the gap?" My answer does exactly that, answer how the lightweight filler is made.

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text:
Light business jets - how many are sold each year?
This AOPA article  says
https://www.aopa.org/news-and-media/all-news/2018/october/16/hondajets-get-performance-upgrades

The company is delivering four to five aircraft a month from its Greensboro, North Carolina, factory, the CEO said. In 2017 and the first half of 2018, the HondaJet was the most delivered light jet in the market. All in all, 92 HondaJets are in service with a 99.7-percent dispatch rate, Fujino explained.

So that's 48 to 60 a year.  What other light jets are available for purchase?

And only $4M USD for a 2016 model that was only flown 120 times (180 Flight Hours Since New. 120 Landings Since New.)  Just need to win the lottery now!  https://www.controller.com/listings/aircraft/for-sale/list/manufacturer/honda/model/hondajet

What do you qualify as a "business jet" vs a personal jet like the Cirrus SF50?

Apparently there are several small jets, most are twins and then the single engine SF50, half the price of the others. https://www.popularmechanics.com/flight/g21098242/best-light-jet-airplanes/  Now I just need those powerball numbers (lottery) to turn out my way ...

For the most recent data available, which is in 2017, GAMA reports that 676 business jets sold worldwide. You can see a breakdown by manufacturer here.
Unfortunately, not all manufacturers detail the models sold. Light business jets typically sell in higher volume, due to their lower cost point. A rough estimate of 60% of sales being light jets would give a rough number of ~405 light business jets sold in 2017. There is no way to ensure this is accurate, but it should give you a ballpark number.

Interestingly enough, a personal jet like the Cirrus SF50 qualifies as a "Very Light Business Jet", which is typically lumped into the Light section. Only 22 were sold in 2017, so that's not a major factor.

GAMA  - General Aviation Manufacturers Assoc. - publishes detailed reports but category and type:
https://privatejetcardcomparisons.com/2020/02/21/private-jet-deliveries-see-big-gains-in-2019/

It's essential to include snippets (properly attributed) because links die or get changed, then your answer becomes meaningless gibberish. Please take the [tour] and read through the [help] to learn about the differences between this Q&A board and a regular "discussion" forum and the standards expected when answering.


text:
Could vortex generators be used to preserve aileron authority during a stall?
I know that using aileron input in the approach to a stall is generally inadvisable; what if vortex generators are placed at the wingtip (where the ailerons sit), meaning that the ailerons will still have roll control authority available even when the rest of the wing is stalled? In this case, would aileron input be permissible?

This question and answer will depend greatly on aircraft—especially wing—design. For example, certain common trainers can be quite stable in a wing stall, with substantial aileron and rudder control. VGs may be one way of aiding continued aileron control, but wingvtwist, or varied angle of incidence, or similar are other common approaches to that problem. See Cessna, Cirrus, and Quest designs.

Okay@J Walters,I will

Are you building a computer model, or are you intending to make a modification to an existing aircraft, or experimental aircraft?

Am actually building an ultralight..... From scratch@KorvinStarmast

Recommend you include that detail in the question, since ultralights have their own unique problems to solve.

Vortex generators re-energize the boundary layer and can slightly postpone flow separation at high angles of attack. Therefore, adding them in front of a control surface is a realistic way of retaining authority. In fact there are real life examples:

[picture by Peter Kämpf]
That being said, these devices are a crutch that is best avoided on clean-sheet designs. They add drag in every flight condition in exchange for some more margin at high alpha, this margin could be achieved by designing the aircraft better in the first place. That is why you will mostly see vortex generators applied as fixes late in the design process or as outright aftermarket modification kits. This constant penalty is compounded by the extra maintenance needed to keep the VGs clean and in good condition.
Ultimately, re-energizing the boundary layer can only do so much to prevent separation. A hard down aileron input at high angle of attack can stall the wing even with VGs, they are not a silver bullet.

I wouldn't dismiss them so lightly. On my Cessna Cardinal, the VGs from MicroAeroDynamics
https://microaero.com/
did wonders to improve the airplane handling at slow speeds - the airplane is responsive at slow speeds now, has the same feel as at higher airspeeds (like 25-30mph faster), and really increased my confidence at low airspeeds.  I used to fly out of a 1680 foot strip, coming in over tall trees. Hot days, low winds, it was a real challenge to get slow enough to get on the runway before midfield and stop before hitting the fence at the far end. After the VGs, it became no problem at all - so much easier to get the plane flying slower and still handle well, it was no problem to be on the ground well before the midfield mark and turning off before the end.
At the other end, there is no noticeable impact to top end speed of around 145mph at 24"mp/2400 rpm.
The only time I stall anymore is during flight reviews with instructors, and I have to really work to get the plane to stall, power off or power on. And when it finally does, just pushing the yoke forward recovers it immediately, with little wing dip to either side. Same with unusual attitude recovery, a little push and aileron correction and straight & level is returned.


text:
Where is the inlet for the APU on a Fokker 70/100?
I can see the exhaust for the APU on a Fokker jet, but where is the inlet?

Can you provide pictures of the specified aircraft please?

You can check this report from the BFU.
I reproduced the image of page 12 of the report here
Obviously, the exhaust is in the middle of the picture and the inlet is on the top right part (trapezonidal shape)

Thanks, my son will sleep better now. That was a tricky one without having a clear photo of it.

You're welcome !

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text:
Is 1 propeller always more efficient than 2?
Based on other answers I've read here (1) (2) (3), a single large blade propeller is the most efficient type of thrust you can get.
There are 2 reasons for this (as I understand it). Firstly, because each blade on the propeller causes wing-tip vortices when low pressure air meets high pressure air.
Secondly, each blade on the propeller adds surface area to the aircraft increasing parasitic drag.
So my question is what if both propellers are surrounded by a duct? Assuming it's a perfect fit, the duct will neutralize wing-tip vortices, so now all that's left is parasitic drag.
Now couldn't you just use 2 propellers that equal the surface area of a single large propeller and get the same efficiency with no added parasitic drag?
On a similar note, could you use just 1 small propeller surrounded by a duct and reach similar efficiency (if not better) than a large propeller surrounded by the same duct?
I say "if not better" because the smaller propeller would have less surface area, thus less parasitic drag.

No, a duct will not cut tip losses to zero.

@PeterKämpf Thank you for that link, so please let me know if this is right. Wing tip vortices are not actually a "big problem" but instead a normal part of lift. The real problem is that lift creates a slightly backward thrust vector which can only be offset by using an elliptical shaped wing. If this is correct why does wing aspect ratio matter? Couldn't you just build a short elliptical wing with a long cord as lift is mainly a matter of surface area and not length?

The aerodynamic force on a wing is always tilted backward; this tilt grows with reduced wingspan. Elliptical wings are not different and suffer the same fate.

Ducts are only used for highly loaded propellers of a very small radius, namely the fan stage of turbofan engines. For lower disk loadings a shroud or duct would create more friction drag than it saves in efficiency.
If the tip Mach number of the propeller is low enough (say below Mach 0.9), then the single propeller of maximum diameter will be the most efficient way to create thrust. This condition is met when both flight speed and thrust per propeller disk area (disk loading) are low.
As the aircraft gets faster, the tip Mach number can best be limited by reducing the propeller diameter. Now more blades will be needed in order to create the desired thrust, and interference between them will reduce efficiency. Also, the higher disk loading will result in more swirl losses, and now it becomes attractive to run a second, counter-rotating propeller behind the first. The two can be either close together or - even better - on opposite ends of the aircraft.

Looking at a static turning propeller blade, as running on a test bench, it is easy to imagine how a one bladed propeller would be most efficient, and how multiblades would not have "clean" airflow due to blade turbulence. This is indeed true and very noticable when one compares fans with props and is popular theory.
However, it is important to realize a prop moving through air follows a helical path in 3 dimensions.
If it is travelling fast enough, than 2 blades will not interfere.  This would be an excellent wind tunnel project.  Also, pitch would play a role, and studying pitch vs "minimum interference speed for x number of blades at various pitch conditions" would be my dissertation du jour, or for many months.
Secondly, single blade props are very tough on bearings and have been known to suffer vibration issues, which are to be avoided as plague in aircraft.
The 2 blade prop can be perfectly balanced and is very efficient.  It is no surprise that it is the blade of choice for light aircraft, with 3 blade also fairly common when ground clearance becomes an issue with more powerful engines.
The 1 blade, although actually applied with low power engines in the past (Piper Cub) yielding some improvement in efficiency, must be balanced with counter weight.


text:
What prevents the use of an EMAS along the sides of a runway?
The NTSB report about the crash of American Airlines Flight 1420 discusses whether an EMAS would have mitigated the severity of the accident, but concludes, based on testimony from a representative of an EMAS manufacturer, that

...the benefit of an EMAS in this accident would have been limited by the airplane traveling partly outside the runway edges; thus, the airplane would not have been able to use the full length of the EMAS. The report also concluded that an EMAS would have reduced the speed of the airplane by 15 knots but would not have enabled the airplane to stop within runway 4R’s runway safety area.  [report page 64/PDF page 78]

What I’m not seeing is any reason why an EMAS would have to be confined to the extended track of the runway; extending it from the ends up along the sides of the runway would provide additional protection for aircraft sliding off, or partly off, the sides of the runway (such as AA1420):

(Aircraft tracks shown in these images are merely examples of possible runway-excursion trajectories, and are not intended to represent any specific flights in particular.)
Am I missing something here?

There are often taxi ways in that area.

Think about what would happen to a plane hitting an EMAS at an oblique angle.

They already do this. Check out the end of runway 8 at KBUR. Southwest demonstrated how this works a few months ago.

@user71659: And that's what I get for relying on a seventeen-year-old report... :-S

I can think of two general reasons not to place EMAS all around the runway. First, it would massively increase the amount of space required for a runway. Some airports might have that space to spare, others might not.
Second, it would cost a lot of extra money. Maybe there are studies on this but even if the money's available, would it be most useful to spend that money on EMAS or on something else? Again, that probably depends heavily on the situation at each individual airport.
In the end, it's another safety cost/benefit analysis. How many aircraft run off the sides of runways? Would EMAS have been helpful in those cases? What are the costs of installing EMAS? Are other measure more useful (and cheaper)? What would be the unintended consequences (like causing ground loops, as Michael mentioned)? Etc.
(There are also possible issues with all the other stuff usually found close to runway edges, like lights, signs and taxiways. Maybe they could be moved somehow, but that would presumably require more space.)

I can think of a couple reasons why you might not want to expand EMAS all around the edges of the runway.  One is simply cost vs benefit:  If it is more likely that an airplane will run off the end of the runway than the edges it would make more sense to put the material there.
EMAS would seem most beneficial in stopping forward speed if the wheels were to make contact uniformly.  An aircraft departing the side of the runway already has directional control problems.  The situation would be amplified if the wheel on the side “pulling” the aircraft off the edge was to be dramatically decelerated.  It could even cause a ground loop.

Also, I am pretty sure that EMAS requires the plane to not be too fast, otherwise either the plane will rip the EMAS to shreds (well, that's the point of EMAS, but I mean without actually doing anything useful) or the other way around, the EMAS will rip the undercarriage to shreds. So, it's designed for a plane that is almost stopping but running out of runway, not stopping a fast-moving plane at the beginning of the landing roll / end of the take-off roll.


text:
Why are cabin doors outlined with a different color than the fuselage?
On almost all airliners I have seen, the doors are painted inside a rectangle which appear to reflect more light. This is the case whether in the aircraft has its manufacturer's paint or an airline's custom livery.
What is the reason behind this?
It can be seen in these pictures.

Image Source

Image Source

Nice question, some really simple that I didn't notice how useful actually is. I learnt something thanks to you.

In almost all vehicle designed to transport passengers (e.g train) doors are painted differently. It make it easier for rescuers to find them.

The doors are painted like this because it is a federal law that all cabin doors on commercial airplanes should be outlined in a color which contrasts with the fuselage color. It is done so that in case of an emergency on ground, rescue crew can find the doors easily and open them quickly.
It happened in past years that passengers survived some crash landings (especially at night) but perished because the rescue crews could not locate the cabin doors in time to rescue them from the burning airplane. The contrasting outlines of the doors allow them to find the doors instantly.

Here is the actual text of this federal regulation:
14 CFR 25.811 (f) Emergency exit marking

(f) Each emergency exit that is required to be openable from the
  outside, and its means of opening, must be marked on the outside of
  the airplane. In addition, the following apply:
(1) The outside marking for each passenger emergency exit in the side
  of the fuselage must include a 2-inch colored band outlining the exit.
(2) Each outside marking including the band, must have color contrast
  to be readily distinguishable from the surrounding fuselage surface.
  The contrast must be such that if the reflectance of the darker color
  is 15 percent or less, the reflectance of the lighter color must be at
  least 45 percent. “Reflectance” is the ratio of the luminous flux
  reflected by a body to the luminous flux it receives. When the
  reflectance of the darker color is greater than 15 percent, at least a
  30-percent difference between its reflectance and the reflectance of
  the lighter color must be provided.
(3) In the case of exits other than those in the side of the
  fuselage, such as ventral or tailcone exits, the external means of
  opening, including instructions if applicable, must be conspicuously
  marked in red, or bright chrome yellow if the background color is such
  that red is inconspicuous. When the opening means is located on only
  one side of the fuselage, a conspicuous marking to that effect must be
  provided on the other side.

Wow, the original CFR actually does use "exists" instead of "exits" in section 3.

@fooot Good find.


text:
What inspection packages commercial airliners follow which make them more reliable than a C-130?
The Hercules C-130 get unserviceable often due to various technical issues. This causes the flight to be aborted (ground or air abort) due to avionics, propulsion, airframe or electric problems. I know that the three level of maintenance include 'O' (organizational or 1st level), 'I' (intermediate or 2nd level), and 'D' (depot level). USAF work cards are followed in all these inspections/maintenance.
I was wondering why commercial airliners, which no doubt are flying more than the C-130s, are rarely seen aborting a mission and diverting to a place other than the destination. Is there a different procedure or plan or work package followed by the commercial airliners which make the flight more reliable?

Welcome to aviation.se. Please refrain from writing in all caps, we are not generating NOTAMs.

Maybe some source would be required to confirm that C-130 is much more unreliable than any other plane. It is produced since 1954 to present, how nobody noticed?

Maintenance regimes are only part of the story. The aircraft design and complexity, age, and of course the type of mission all factor into aircraft reliability.

I would guess that not being shot at makes a difference, too.

As mentioned, factors like a different mission are much more likely to be a reason for any difference in reliability. Military aircraft often fly a harsh mission, the pilots don't fly to extend life, they use max power on every takeoff, fly at a high power setting, and run the engine closer to its temp limit. They aim to get there fast, and the C-130 flies into dirt strips, where the dirt gets ingested into the engines. In comparison, commercial airlines operate with a very close eye on the bottom (financial) line. They take-off derated if they can, and fly with a very simple cruise profile. They do not perform high speed tactical descents that a military C-130 would, into an airport possibly surrounded by hostile forces with air to ground weapons.

It is certainly true that military aircraft often operate in harsher conditions than commercial airliners, creating more wear and tear. But they could still be made more reliable. It comes down to how much the operator is willing to pay for a higher reliability, in terms of up front cost and performance.
Commercial airlines are running a business. They pay a lot for their aircraft, and every minute that the airliner isn't moving passengers from A to B is lost revenue. This causes inconvenience for the passengers and expense for the airline. Passengers tend to choose the airline that is cheaper and less likely to leave them delayed. And every dollar spent on maintenance comes out of profit. Similarly, manufacturers are competing to provide more reliable aircraft. They spend a lot of time ensuring their designs will be reliable, and improving designs based on service experience.
The military is in a different situation. Passengers or cargo is not at much risk of choosing a different carrier based on cost or reliability. And for willing to allow lower reliability, the military can trade it for lower upfront costs and higher performance. This means they can carry large cargo, make short takeoffs, climb quickly, operate unpressurized, make steep approaches, land harder on rougher ground, and stop quickly.
Age is another factor. Airlines in the US have average fleet ages of around 10 years (with some outliers on both sides). The active duty fleet of C-130 aircraft has an average age of 25 years. While military airlifters may fly fewer hours, age still factors into maintenance. Components break down over time. Newer planes will have the latest design updates and be less likely to develop issues.

I don't think it makes a lot of sense to try to compare military aircraft (in general) to airliners. There are just too many differences in what's expected of them and how they're used to make a comparison at all meaningful.
Compared to other military aircraft, the C-130 doesn't stick out as doing particularly poorly in terms of mission readiness (nor does it stick out as doing unusually well)1.

On the other hand, if your standard of comparison is the C-17, then it's absolutely true that the C-130 looks fairly poor in comparison. A difference of roughly 10% in readiness rate might not initially seem particularly terrible. In reality, it's probably more reasonable to think in terms of the number that aren't mission capable at any given time. A C-130 is nearly twice as likely as a C-17 to be down for maintenance at any given time. That's balanced to some degree by the fact that we have a lot more C-130s though.

1. https://www.airforcetimes.com/news/your-air-force/2018/03/05/fewer-planes-are-ready-to-fly-air-force-mission-capable-rates-decline-amid-pilot-crisis/

i was going thru the mission capable rate of C-130 H and C-130 J. what is the reason for such low reliability? what all issues are resulting in this low rate


text:
Why do propellers have less theoretical range (i.e. range ignoring impatient passengers wanting to go fast) than jets, despite greater efficiency?
I was playing around with the breguet range equation recently, and came across a suprising result, that propellers have less range than jets, despite having greater efficiency.
The range equation for a prop is:
R = 550 * np * ((L/D)/(C / 3600)) * ln(Wi / Wi+1)
where C is the SFC, in lb/(hp * s), and R is the range, in feet. Note that the 550 here coincidentally is the same as the speed in the next calculation, but the 550 here is actually a conversion factor from hp to lb-f/s
According to wikipedia, the most efficient turboprop engine is the NK-12, used on the Tu-95 bomber (and Tu-114 airliner), and that engine gets a SFC of 0.36 lb/(hp*h). Assume a propeller efficiency of 0.8, which is typical.
R = 550 * 0.8 * ((L/D)/(0.36 / 3600)) * ln(Wi / Wi+1)
R = 550 * 0.8 * ((L/D)/0.0001) * ln(Wi / Wi+1)
R = 550 * 0.8 * ((L/D)/0.0001) * ln(Wi / Wi+1)
R = 4400000 * (L/D) * ln(Wi / Wi+1)
For jets:
R = (V / (C/3600)) * (L/D) * ln(Wi / Wi+1)
a SFC of 0.5 lb/(lbf*s) in cruise is considered pretty good for jets, and let's assume a 550 mph cruise speed (or 806.667 ft/s). Range is now:
R = (806.667 / (0.5/3600)) * (L/D) * ln(Wi / Wi+51)
R = 5808002.4 * (L/D) * ln(Wi / Wi+1)
The range expressions for jets and props is identical, except for the coefficient, and 5808002.4 is greater than 4400000, so therefore, jets have better range, even on paper, than props, assuming same L/D ratio and fuel ratio. This is kinda suprising, given that props are quoted to have higher efficiency than jets. I've heard people say props have less range, but I've always heard it backed up with the evidence that "props are slow, and people like to go fast". Are my calculations and data correct? If they're correct, why, intuitively, do props end up having less range?
Clarification: user3528438 has pointed out that some turboprop engines provide both a power specific fuel consumption number, as well as thrust specific. However, if you plug the thrust specific fuel consumption number for that turboprop into the jet range equation (essentially treating the prop as a jet), the resulting range is very different than the range you'll get if you plug the power specific fuel consumption number into the propeller equation -- so which one is right? I doubt my formula for propeller range is wrong (though I might be using it wrong - could someone please check) because the same formula (but without the conversion factor, because they're using metric) is found here - https://nptel.ac.in/content/storage2/courses/101104007/Module2/Lec8.pdf.
I also have my derivation of the formula on hand too, if anyone wants to check that.

Does this answer your question? Why don't airliners have turboprop engines instead of jet engines?

@ManuH Pretty sure it won't - 1) the question here is very specific, and 2) the old question was quite different, even if the one it was a dupe of can be useful.

Yet the longest range aircraft, the Rutan Voyager, had propellors: https://en.wikipedia.org/wiki/Rutan_Voyager

This isn't an internet forum; changing your question based on an answer breaks the principle methodology of the SE model.  If you want a threaded discussion, go to a forum. If you find the question has problems, it is better to write a new, better, question.  [Tour], [Ask] and [Answer] provide more guidance.

Update
As @Zeus has pointed out correctly: Drag coefficient stay constant in my scenario, not drag -- I've updated the explanation accordingly. Sorry for that blunder. The conclusion does not change: Engines with constant PSFC only have an advantage when flying slowly and get worse much quicker than engines with constant TSFC -- but actual engines are mostly in-between these days.
As others have pointed out already, the important thing to note is that propellers have (roughly) constant PSFC (specific fuel consumption per power output), and jets (roughly) constant TSFC (specific fuel consumption per unit of thrust).
(The second thing of note: quoting equations which include unit conversion factors is dangerous, and doing so without specifying which units are used is doubly so.)
Power is thrust times velocity, which means that although a propeller can have a much higher propulsive efficiency (propulsive power vs shaft power), it also scales quite differently with speed, even ignoring the fact that propellers have difficulty operating above Mach 0.6:
Assume we have a series of aircraft, each designed to fly at a particular speed (all well below the speed of sound), with the same glide ratio and the same weight. This means they all fly at the the same drag coefficient, and the required thrust scales with the square of speed. Now we decide which kind of engine to use for which one of them.
Let's design a family of jet engines, each of which delivers a certain thrust, and all of which have the same constant TSFC. This means 1 Newton of thrust costs the same amount of fuel per second, independent of how fast you're going.
The fuel flow would of course still increase with the square of velocity because you would need more thrust the faster you're going. And that means that fuel burn per distance travelled would increase proportional to speed. Most jet airliners are actually flying faster than their best glide ratio (= lowest drag coefficient) would suggest, because that minimizes fuel per second, not fuel per distance. They're even flying a bit faster than what they@d need to do to get minimum fuel per distance because for an airline, time is money. That's why they're burning a bit of extra fuel in order to arrive faster and do more flights with fewer aircraft.
Using propellers with reciprocating engines, though, although they're converting more of the shaft power to thrust, the fuel flow through the engine scales with power, not thrust, and power needed for constant thrust scales with velocity. So doubling speed at equal thrust requires twice as much fuel per second, but since thrust increases with the square of velocity, fuel flow actually scales with the cube of velocity. So fuel consumption per distance scales with the square of velocity, proportional to drag (still assuming the same drag coefficient for all aircraft, of course).
That's why the most efficient propeller aircraft would be flying at the minimum drag, i.e at their optimum glide ratio, fairly slow.
Going faster gets expensive quick.
So however efficient your propeller is at some (low) speed, the faster the aircraft for which you want to decide on an engine, it will eventually be worse off than a jet because its fuel per distance quadruples when doubling speed, but the jet's only doubles. At whichever velocity our fictional jet engine and piston/propeller get equal fuel economy, the move to the next-faster airraft with a propeller will be twice as expensive as with the jet. And at the same time, the same aircraft with a jet will be flying faster, too.
That's the reason why piston engines with propellers are the weapon of choice for long-endurance flights, where distance covered is less important than time afloat, or where costs are more important than speed. In such cases, a jet would get much worse range!
However, most larger propellers are driven by turboprops these days, and turboprops do not have constant PSFC, since they have a turbojet core providing the shaft power, which benefits from the increased pressure of air in the intake at higher velocities. And modern high-bypass turbofan engines don't have constant TSFC, either, since they have more losses in the bypass duct at higher velocities at constant thrust. In fact, an extremely high-BPR turbofan starts to approach the  characteristics of a comparably low-BPR turboprop (except at large Mach numbers, but we're still ignoring that here).
Conclusion
It's dangerous to confuse TSFC and PSFC. An engine with constant PSFC (old-fashioned piston-driven propeller) might fly a lot more efficiently at low speeds but gets worse quicker than engines with constant TSFC.
Because nobody (except for this guy -- who is amazing) wants to take days to finish their intercontinental flight, and because propellers don't work so well at higher Mach numbers, commercial long-range flights fly at speeds at which jet engines (that is: Turbofans) use less fuel per distance than propellers with reciprocating engines, and they get higher range in those circumstances. For high-efficiency flying over long distances, where speed is not that important, however, Propellers are still popular, and have better efficiency. See for example auxiliary engines for sailplanes, or most military transport aircraft. For the latter, range is everything, speed (and noise...) are secondary. However, since those are built to military specifications, they're not that useful as civil cargo aircraft, and since the civil cargo aircraft market is very small, most of it is covered by converted passenger aircraft. If there were dedicated civil cargo aircraft of similar size as long-range passenger jets, they'd probably fly much slower and use turboprops (noise regulations permitting...).
Aside
Another issue with piston engines is that their performance reduces the higher the fly, as the air thins. This issue can be reduced by adding a turbocharger, but a jet engine already is essentially a very big turbocharger with a turbine attached. The other advantage of jet engines is their power-to-weight ratio. This is why e.g. most helicopters don't use piston engines and have turbines instead.

"Doubling speed at equal thrust requires twice as much fuel per second." Formally correct in the context, but how do you do that? By slashing the drag coefficient 4 times?

@Zeus: Yikes! You're right! c_D stays constant but drag increases of course ... Will correct the scenario asap

For more background, this question is about the usage of Breguet Range Equation (I find this explanation better suited for this question)
There are many problems with your calculation:

Time unit of speed should be the same as the time unit of SFC. For your first calculation, since you used mph for speed and lb/(hp*h) for SFC, your SFC term shouldn't have 1/3600. For your second calculation, since your speed is fps and your SFC is also in lb/(lbf*s), there's no need to have 1/3600 either.
For both calculations, end result should be the same unit of length. Your first calculation uses mph and the second uses fps, so the the end result would be in miles and feet so not comparable. But since you made the mistake #1 you end with numbers still on the same order of magnitude.
For the propeller case you are using PSFC (Power specific fuel consumption) rather than TSFC (Thrust-specific fuel consumption). Breguet Range Equation requires TSFC to work.

If you look at the Breguet Range Equation you see the only difference between prop case and jet case is TSFC. So to compare relative range differences, you only need to compare TSFC and avoid all other complications.
Take Cruise TSFC from some modern examples:

GE90: 0.545 lb/lbf/h
Europrop TP400: 0.38 lb/lbf/h

(1/0.38)/(1/0.545) - 1 = 43% so with everything else being the same, prop should have about 40% more range than jet.

I believe you're misinterpreting the 550 in the 1st calculation, the 550 is a conversion factor from horsepower (which is never used in calculations) to ft-lb/s, which is the one used (imperial is weird in that lots of units are used in data, but not used in calculations, e.g. mass is written in lbs, but in calculation, you use slugs, power is written in hp, but in calculation, you use ft-lb/s). Sorry for picking 550 mph as the speed, that was confusing, my bad.

I didn't see that some turboprops also have TSFC data, I guess I'll plug those into the range equation, and the results you get make more intuitive sense (props SHOULD have more theoretical range). I just redid my derivation of the range equation for propellers and the results still don't match yours, but I guess finding the error in that derivation is another can of worms, more fit for the physics stackexchange.

I think there are some confusion here, in particular, as @user3528438 said, with units used in formulas. I'll also try to highlight problem with another point of view.
1. Formulas comparison
First of all, be really careful when using the first formula. At first, I thought it was not consistent regarding range R units. The way you make calculation formulates the range on « ft2.s-2 ». After taking a look on the demonstration of the paper you shared, I realised that the SFC is here defined as « Newton of fuel » / « Power x time ». It seems it does not provide any error here cause your SFC uses lbs and it is equivalent to pound force lbf.
Then, it is important to notice that both formulas say exactly the same thing ! There is not a « jet range equation » or method « treating a turboprop as a jet » :

One consider Power SFC whereas the second use Thrust SFC (Pwr = T.V and so PSFC = TSFC/V).
An other difference is the efficiency in the first equation. Not sure about it, but it seems to comes from the SFC definition again. In the paper, the author define the power as the power used by « reciprocating engine » which mean available input power. It could be electrical power or chemical power in burner. That's why they need to include the efficiency.

Note that, it is not just the propeller efficiency but the overall system efficiency (including thermal and propulsion efficiency for a gas turbine) as it is defined like « input power » / « aircraft power ». For me, it is more convenient to include it in SFC data (at least, I guess it is in data we can find online).

2. SFC definition
Here we have 2 definition TSFC and PSFC, introduced in the previous section, both sometimes called Specific Fuel Consumption:

TSFC: 1 lbs/(lbf*h) of SFC means the engine will consume 1 lbs/h fuel for each pound force of thrust provided.

PSFC: 1 lbs/(hp*h) of SFC means the engine will consume 1 lbs/h fuel for each horsepower (or 550 lbf.ft/s) provided.

According to wikipedia, a power is the rate of a system doing a work or providing energy by units of time. In our problem, it's a measurement of how fast a mechanical work is given to the aircraft by the engine (e.g. T x V).
Now take a look about your applications:

In your specific case, you compare 2 engines: the first one is a turboprop with a SFC specified in power definition = (c/eta) = 0.36/0.8 = 0.45 lbs / (hp * h). The second is a turbofan with 0.5 SFC in thrust used during a steady flight of 806.667 ft/s speed. So we can calculate its PSFC = 0.5 * 550/806 = 0.34 lbs / (hp * h). The quotient 0.45/0.34 is what you got (e.g. 5808002.4/4400000). Several things to note:

data used for turboprop SFC does not match with first formula definition (at least, I'm pretty sure that eta is already include in the value 0.36 lbs / hp*h.

your turbofan as a better PSFC and provide more power with same fuel or need less fuel to provide same power that's why the range is bigger.

Remember that the data you find SFC = 0.36 lbs/(hp * h) is equivalent to a SFC = 0.36 lbs / (lbf * h) for a flight speed of 550 ft/s. Now, let's try to put the turboprop in same conditions than the turbofan (e.g. 806 ft/s).

if we keep TSFC = cst: we can compare range directly and we got about 40% more range for the turboprop. Is what's @user3528438 made in his answer.

if we keep PSFC = cst: we can calculated the TSFC at this specific flight point (806 * 0.36 / 550 = 0.527 lbs / (lbf * h)). Here, the turboprop provide a slight increase of range.

So which case is the true one ? Probably none of these.. Intuitively, I want to say a turbofan has more chance to keep TSFC constant when changing flight condition while is PSFC for a turboprop. Indeed, you can try to reduced little by little the speed condition and find the limit where it's preferable to have a turboprop rather than a turbofan. But it is huge assumptions here so I'm not confident with results. Nevertheless, it could be interesting to compare it with flight speed of most aircraft equipped with turboprop.
However, this provide a first explanation why turboprop is usually operating at low speed. The other reason is a propeller need to have large diameter to be really effective and give enough thrust. Therefore we got an aircraft speed limit at the point where the flow become supersonic at blades tip. You can still reduce the rotational speed but it could be difficult to reduce it even with gearbox without affecting overall gas turbine efficiency.
Conclusion
In conclusion, SFC is an important parameter of engine performance. But it is good to keep in mind that it is calculated for specific design points (e.g. flight conditions) thus dependent of the aircraft mission. SFC is specially used for comparing 2 engines designed for same aircraft.


text:
Why can some aircraft not fly near the north pole?
The Adiru on the Airbus 320 has an limit like 84°N latitude. What happens if the plane is flown above that latitude?

Hello, where do you take this limit from? Could you be misled by the limits related to magnetic heading computation area?

Related: Can you fly with INS/ IRS at higher lattitudes?

I am retired and no longer have access to the aircraft manuals, but I believe the B777 is not certified to fly over the True North Pole.

You don't get a valid heading and track angle. Each ADIRU model has different characteristics and limitation. This is an example from an FCOM that I have:

Special flights can fly in these conditions, but they don't use magnetic headings (see this question).


text:
What are the differences between Cat I, Cat II, and Cat III as concerns aircraft requirements?
I understand that Cat I, II, and III ILS approaches have progressively smaller weather minimums. However, I am asking about the aircraft themselves. What are the differences between Cat levels as concerns aircraft equipment requirements and approvals?

Why the downvotes? This is an excellent question!

We already have a question about the differences in the approaches, it makes sense to have one about differences for the aircraft as well.

As seen in the question that @fooot referenced, these two FAA AC documents seem to have information that might provide the answers: see AC 120-29A for Cat I & II, and AC 120-28C for Cat III.

If you want to deep dive in the topic, this Airbus publication is a good one: Getting to grips with CAT II / CAT III operations, on SKYbrary. Look at chapter 4, Aircraft Requirements, page 99.

The differences are in the demonstrated accuracy of the ILS or RNAV equipment. Not sure if the question can be properly answered without writing a book, but digging into the documents linked by Jonathan Walters I extracted the tables below. The document is very long and full of caveats, exceptions and specifics on testing requirements, etc. and frequently refers to parameters set forth in other documents.

CAT I

Source

CAT II

Source

CAT III

Landing System Performance.   All types of low  visibility  landings systems, including  automatic flight control, guidance for manual control, and hybrid, shall be demonstrated to achieve  the performance accuracy  with the probabilities prescribed in this section.  The performance values may  vary  where justified by  the characteristics of the airplane.
The performance criteria and probabilities are as follows:

(a)  Longitudinal touch down earlier than a point on the runway  200 ft. (60m) from  the threshold to a probability  of 1 x 10-6;
(b)  Longitudinal touch down beyond 2700 ft.(823m) from  threshold to a probability  of 1 x 10-6;
(c)  Lateral touch down with the outboard landing  gear more than 70 ft. (21.3m) from  runway  centerline to a probability  of 1 x 10-6.
(d)  Structural limit load, to a probability  of 1 x 10-6.  An  acceptable means of establishing  that the structural limit load is not exceeded is to show  separately  and independently  that:

(i)  The limit load that results from  a sink  rate at touch down not greater than 10 f.p.s. or the limit rate of descent used for certification under 14 CFR part 25 subpart C (see section 25.473), whichever is the greater.
(ii)  The lateral side load does not exceed the limit value determined for the lateral drift landing condition defined in part 25, section 25.479(d)(2).

(e)  Bank  angle resulting  in hazard to the airplane to a probability  of 1 x 10-7.  A hazard to the airplane is interpreted to mean a bank  angle resulting  in any  part of the wing, high  lift device, or engine nacelle touching  the ground. 6.3.2.  Speed Control Performance.   Airspeed must be controllable to within +/- five  knots of the approach speed*, except for momentary  gusts, up to the point where the throttles are retarded to idle for landing.  For operations flown with manual control of approach speed, the flightcrew must be able to control speed to within +/- five  knots of the approach speed.

Source


text:
Is it better to begin the gear down before landing checklist abeam the touchdown point or midfield?
For complex aircraft, I had always been taught to begin the before landing checklist, or the gear down before landing checklist, abeam the touchdown point, which for me is normally the thousand foot markers. However, I recently heard a DPE say to begin the checklist at midfield.
Which is the appropriate method? There could be many opinions offered on this; however, opinions aside, what might be the considerations that would lead to beginning the checklist sooner? Is there a prescribed point to begin the checklist that I have overlooked, for example in the Practical Test Standards or elsewhere?

I suspect the DPE's point was that you shouldn't rush or let yourself get behind the aircraft, and putting the gear down slightly earlier may help with that, especially with a short runway, non-standard pattern or other 'distracting' situations. The C182RG POH actually recommends extending the gear before entering the pattern, to give yourself more time to confirm it's down and locked. I don't think there's any 'rule' here, it comes down to what you're comfortable and safe with.

Anything that makes you comfortable. I agree with Pondlife - the best time for gear extension is subject to the pilot's skills, specific aircraft type & approach complexity. E.g. if it's a tight pattern due to high terrain surround all sides, you may want to extend the gear (or even do the whole landing checklist) earlier.


text:
What information might go in the remarks section of an IFR flight plan?
When filing an IFR flight plan, what information might go in the "Remarks" section?

The remarks field, also called ITEM 18 field on ICAO flightplans can take a lot of information that you as the pilot deem necessary for controllers or authorities to know about your IFR flight.
The list of possible items in an ICAO flightplan ITEM 18 field is available over at the Skybrary, but here are a few examples that are commonly used:

(c) “TYP/” followed by type(s) of aircraft, proceeded if necessary by number(s) of aircraft, if “ZZZZ” is inserted in Item 9
Example: TYP/2 DE HAVILLAND HERON. Up to 60 characters may be used.
(e) “ALTN/” followed by the name of alternate aerodrome(s) or bearing and distance to navaid/navigation point closest to alternate point, if “ZZZZ” is inserted in Item 16. Up to 100 characters may be used.
Example: ALTN/MEDIUM AIRPORT
(k) “OPR/” followed by name of the operator, if not obvious from the aircraft identification in Item 7.
Example: OPR/BIG COMPANY
(o) “RMK/” followed by any other, plain language, remarks when required by the appropriate ATS authority or deemed necessary. There is no limit in number of characters to be used.
Example:RMK/TRAINING ILS APPROACH AT SMALL AIRPORT
RMK/STUDENT SOLO FLIGHT

It is also common to put Overflight numbers on there, to keep ATC from asking for them.

No SID/STAR if flying a small airplane and can't make the required climb gradients.

Not necessarily just a small airplane.  You should include this remark any time that you do not have the SID/STAR charts on board.

Put anything that you believe would be relevant for the controllers to know, but not recorded in other fields.  For example, you are filing from XYZ to XYZ to shoot practice approaches.  You can put that in the remarks, noting airports where you want to practice.  This will help ATC handle your flight.

Around the Great Lakes it is common to put "NO OVERWATER" if you don't want to be routed over the lakes.

First, ATC does see the remarks section of your flight plan. You should use it for anything that you, as the pilot, deem relevant to your flight. As a 34-year retired Chicago Center controller and lifelong flight instructor, I have taught students to use this on every flight.  NO SIDS/STARS; NO OVER WATER; VFR GPS; NEW INSTRUMENT PILOT, etc. In the controller world, a new instrument pilot is held to the same standard as a veteran airline pilot because we have no way of knowing the difference - unless you tell us.  Controllers are always trying to be efficient by turning aircraft onto final as close to the "approach gate" as possible. This works great for seasoned IFR pilots but for new guys - not so much. The localizer is flight checked to 18 NM. A longer final for a new IFR pilot offers an opportunity for a more stable approach. Why not put "REQUEST EXTENDED FINAL APPROACH" in the remarks section? Just a thought.

In helicopters, IFR flights can often terminate in S-VFR.
In this example, one might add "Request S-VFR from HELOG to Downtown"


text:
Is there a maximum or minimum temperature for take-off and landing?
Is there a maximum or minimum temperature that a plane can take off or land at?

Be aware there's not just a max air temperature for some aircraft, but there are sometimes max temperature limits for the fuel. For example the 747-100/200 limit was, as I remember 54.5C (130F). Same for the -400. See http://b747400.com/pdf/limits.pdf. Back in the 1990s in the Arabian Gulf countries during summer, this was sometimes a problem.

I used to work as a load planner for UPS, and often aircraft was grounded well before approaching any max limit, because in order to fly a large aircraft like a 747 (for profit) you would have to de-fuel or unload much of the cargo, so we would just hold the plane until air temperatures cooled so we could fly it fully loaded, and take the hit on the delay.  I was also, once bumped from a flight from PHX to HNL due to density altitude issue because of the heat.

There is a maximum temp but that varies by airport altitude, runway length, aircraft and payload. You can find an answer to that question here.
There is not really a minimum temperature but it needs to be warm enough out to run the engines. Again this varies by aircraft and a preheat can usually solve this problem but there are places on earth where it be comes practically to cold to operate some aircraft. On a similar note if icing conditions prevail you are not really going anywhere but those can occur at lots of altitudes and temperatures. If the given airplane is stored outside and the airport lacks proper de-ice equipment you may be grounded.

Maximum and minimum temperatures are governed by two factors.
First, there is the limitations imposed by the manufacturer.  For example, recently the media has been reporting that some regional jets have max temps for operations, and they have been unable to operate in the southwest US.  Some manufacturers also limit low temperature operations, and may require different lubricants, fuel, etc.
Second, aside from manufacturer (or company) limitations, there are practical limitations. Engines can be hard to start at -40.  Fuel can gel. Batteries can render insufficient power to perform normal starts.  These limitations are normally determined by practicality, experience or other sources of information by the crew.
In my experience, dealing with hot soaked planes is normally easier than dealing with cold soaked planes.  Other issues like density altitude (DENALT) are operational issues, that while normally are considerations, are usually not hard limitations. For example, departing a 1200 foot strip in South American mountains on 35C days has been a limitation with a turboprop aircraft, for me, but the number of times I have had those operational considerations limit flight can probably be counted on my fingers and toes.
So in general, there are two limitations: Those imposed by the manufacturer and the aircraft certification, and those imposed by practicality (which includes best practices).

Perhaps this should be a new question, but I've read two things regarding the regional jets in Phoenix. I've heard "they can't take off because the runway isn't long enough", but I've also read "the POH (or something similar) tables don't give data above a certain temperature, therefore they can't fly (even if the runway would be long enough for the conditions), and updating the tables with new information would allow flight". Any idea which it is, or both?

I know that some of the flights are impacted by a max operating temperature. I don't have an authority on the details, but I think it is something like a 119F ambient.

The runways are about 10,000' long.  It is possible that the runways aren't long enough to satisfy the runway length requirements (significantly more runway is required than is actually needed to take off) but it is more likely that the performance charts don't have performance numbers above a certain temp.  It got up to 121°F/49.5°C in certain parts of Phoenix on 6/20 so it is very possible that crews simply could not calculate performance which means they were not legal to fly.

Yes, there are some temperature limitations, but these are typically aircraft specific.
For example, the Beechcraft King Air B200 has the following limitation:

Max Outside Air Temperature Limitations
Sea Level to 25,000 FT pressure altitude:     ISA + 37° C

These limitations are given in the AFM, and compliance is required.
Practically speaking, this limits aircraft operation of any kind—including takeoff and landing. Takeoff would not be authorized at sea level above 52°C, or at 5000 ft pressure altitude above 42°C.
For a minimum temperature, the engines have a starting limitation of at or above -40°C.

It depends on the model of the plane, particularly its engines, the length of runway available, and surface wind conditions. The aircraft's Pilot Operating Handbook will include a set of performance charts. To determine whether you can safely takeoff or land, you would plot the values (including temperature) into the chart.
This related question discusses some of the precautionary steps one should take when operating in very cold or hot weather.
In general, aircraft performance will be the limiting factor in hot weather, and in cold weather the challenge is to get things started and stop things from freezing.
There is no absolute temperature regulation-wise. Practically you can argue that the minimum temperature is when the fuel freezes and the maximum temperature is when the tire melts, but you will likely run into other troubles before this extreme is reached.

There are regulatoty limits. Air carriers must adhere to performance charts. Charts only go to 48°c? No flying at 49°c.


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How is TAS affected by wind?
Does True Air Speed (TAS) change with wind speed and direction?
My understanding is that if an aircraft were travelling at 470kt TAS, with a hundred knot tailwind, the ground speed would be 570kt. In this case the TAS would remain the same, regardless of the wind, but the ground speed would change.

True airspeed is relative to the air mass you are flying through, so yes, TAS is not affected by wind speed.

Note that sudden changes of the wind speed do affect the TAS. Due to the inertia of the aircraft instantaneous changes in groundspeed are impossible.

The key here is, like most everything else in Physics, TAS is not an absolute value, it is ALWAYS* relative to the speed of something else! So how does your "Train Velocity [Speed]" vary with the speed of the train? Or your "Earth Ground" velocity change as the earth rotates? All velocities/speeds are relative!

True airspeed refers to the actual speed which the aircraft is moving through the air.  Ground speed is the speed at which the aircraft moves over the ground.  The formula
$v_\text{ground} = v_\text{true} - v_\text{wind} \cdot \cos(\alpha)$
Where

$v_\text{true}$ is the true airspeed
$v_\text{ground}$ is the groundspeed
$v_\text{wind}$ is the magnitude of the winds aloft
$\alpha$ is the angle of the winds aloft relative to the longitudinal axis of the aircraft.

This answer is unclear.  A sudden or instantaneous increase in tailwind will briefly decrease the TAS but then it will return to where it was before.  A slow gradual increase in tailwind would have no discernable effect on TAS at all.  Also, if an aircraft is circling at a constant bank angle, causing the tailwind / headwind component to rise and fall, this has no effect on TAS, no matter how tight the circle (i.e. no matter how rapid the change in the tailwind / headwind component).  (As to how this last bit as possible, might be best suited to another ASE question!)

I have no idea what’s going on with this stuff. People keep editing this stupid answer and I wish they would not.

I've locked the post, which will prevent further edits. (The content of the post isn't actually in dispute, but that's what the boilerplate text says, and that text can't be changed.) If the author would like to make edits, you can flag the post for moderator attention with the request to unlock it, and any mod can do that for you.

Aircraft travel within air and they are only connected to that air mass*. Lift, drag & thrust are caused by interaction with this air mass. That's why measuring the aircraft's speed in relation to the air is of importance.
Wind is simply the movement of the air mass over the ground. If the wind is steady, or put otherwise, the air mass is moving steadily over the ground, the speed of the aircraft through the air is not affected since there is no connection with the surface of the ground and the plane.
If, however, there are sudden changes in the direction and/or the speed of the wind (the air mass), the true arispeed of the aircraft will fluctuate accordingly. For example a sudden increase in tailwind will decrease the true airspeed momentarily untill the thrust from the aircraft's engine(s) has accelerated the aircraft back to equilibrium of thrust and drag.
*and gravitation, but in this case we can disregard the gravitation


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Has FAA published any A-RNP STAR or A-RNP / RNP AR DP SID?
After reading FAA's Performance Based Navigation Strategy 2016, I tried to search for already published Departure Procedures of RNP specification. I could only find some that require RNP-1, even though they seem to be rare, like STAYY ONE (KSNA airport).
My question is, are there any SIDs of A-RNP or RNP AR DP specification or STARs of A-RNP specification officially published, at least as far as FAA's charts are concerned?

Did you look for procedures here or someplace else?  https://www.faa.gov/air_traffic/flight_info/aeronav/digital_products/dtpp/

@CrossRoads thank you for your input, I have already used the link you specified in order to search for FAA's published Departure and Arrival Procedures. I also checked the Coded Instrument File Procedures (CIFP) file provided by FAA. My understanding is that no A-RNP or RNP AR DP procedures (SID or STAR) have been published yet.


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Does 'Fat Albert' Have any significant modifications?
The Blue Angels use a C-130 known as 'Fat Albert' in some of their shows. Other than the paint job and smoke, are there any significant differences between 'Fat Albert' and a standard C-130?

I will preface this by saying that I could be wrong.
I know that the USAF Thunderbirds' F-16 aircraft are not modified other than paint and smoke capabilities. I'm pretty sure that the Blue Angels' F/A 18s are the same, so, by extension, the Fat Albert C-130J should have only have paint modifications, and perhaps smoke or other show mods. The older Fat Alberts were equipped with JATO/RATO pods, the new one isn't because it doesn't need them, as it has more powerful engines, and reduced availability of the rockets. All of the C-130Ts were grounded due to an accident in 2017, which included Fat Albert, and the Navy and Marine Corps decided to reduce the C-130T fleet in favor of a C-40 Clipper, (A military B737-700). At the time, the RAF was selling a C-130J, and the Marine Corps purchased the aircraft, removed the RAF modifications, re-painted it, and it became the newest Fat Albert. Incidentally, Fat Albert is assigned to the Navy's Blue Angels squadron, but is a USMC aircraft, and the crew is all Marine.
So, the TL:DR is no, it doesn't have significant modifications.

I can vouch for this answer being correct.  Years ago I was a C-130 loadmaster and several of my friends crewed on Fat Albert.  We met up and walked around inside the airplane while it was in town for a show.  No difference except for paint.


text:
What happens at the wings when the yoke is pulled backwards?
What happens at the wings and vertical stabilizers when the yoke is pulled backwards or forward on typical airliners like the Boeing 747-800.  Is it any different for smaller similarly shaped aircraft like private jets?

Related: Why do airplanes lift up their nose to climb? and also How do elevons work to roll a flying wing?

Pull back, cows get smaller; push forward, cows get bigger.

@Korvin, hah! that brings back memories, My first instructor in USAF UPT told me the exact same thing.  Only it was the stick not the yoke, and houses, not cows. ..

@KorvinStarmast Keep pulling back, cows get bigger.

Most aircraft have control surfaces that work in a similar manner from a little Piper up through a 747. Forward and back movement of the yoke or stick typically results in actuation of the elevator. For aircraft that have the common style empennage the wing remains unchanged. For aircraft that have elevons they move accordingly.
Pulling away from the front of the aircraft on the control column causes the aft end of elevator to move upwards relative to the airframe. This action causes the aircraft to pitch nose up.
Pushing towards the front of the aircraft on the control column causes the aft end of the elevator to move down relative to the airframe. This action causes the aircraft to pitch nose down.
Take a look at this GIF for a nice animation or this video.

Would it be more accurate to say pulling the yoke/stick towards you pulls the nose towards you, and pushing it, pushes the nose away from you, rather than thinking in terms of up and down?

@BillDOe I don't think so, seeing as how the distance between the nose and the pilot is fixed. Saying "nose towards you" to mean "nose up (relative to the aircraft)", and "nose away from you" to mean "nose down (relative to the aircraft)", doesn't make intuitive sense to me at all. If anything, maybe it should be "nose towards the ceiling" and "nose towards the floor"?

@BillDOe: I see what you mean, but if pulling the control column makes an airliner nose going down, you are in serious trouble, regardless of the reason (flying inverted, vertical, or stalling).

@TannerSwett, I'm suggesting that thinking outside of up and down (i.e. nose going towards the sky and towards the ground) may be confusing in inverted flight, where you'd need to push the yolk/stick to get the nose pointed upward, and vice versa.

@mins, if you're in regular right-side-up flight, the horizontal stabilizer is pointed up, towards the vertical stabilizer. If you then go inverted, the horizontal stabilizer is now pointed down in the same direction as the vertical stabilizer. Am I getting something wrong? I'm asking, not arguing.

Oops! When I said, "pointed up" I was thinking of the trailing edge.

@BillDOe I think mins's point is that in an airliner, if you're in inverted flight at all, then you're in serious trouble.

@TannerSwett, thanks. In that light, I see the point.

Moving the yoke forward/backward moves the control surfaces on the elevator. In most aircraft forward/backward yoke movement has no impact on the wings and vertical stabilizers.

Hmm...so it doesn't affect the AoA on the wings?